Does Computerized CT-based 3D Planning Of The Humeral Head Cut Help To Restore The Anatomy Of The Proximal Humerus After Stemless Total Shoulder Arthroplasty?

BACKGROUND Restoration of proximal humeral anatomy (RPHA) after total shoulder arthroplasty (TSA) has been shown to result in better clinical outcomes than is the case in non-anatomical humeral reconstruction. Preoperative virtual planning has mainly focused on glenoid component placement. Such planning also has the potential to improve anatomical positioning of the humeral head by more accurately guiding of the humeral head cut, and selection of anatomical humeral component sizing. Hypothesis of the study: The use of preoperative 3D planning helps to reliably achieve RPHA after stemless TSA. METHODS One hundred consecutive stemless TSA (67 males, 51 right shoulder, mean age of 62 ±9.4 years) were radiographically assessed using pre- and postoperative standardized AP radiographs. The RPHA was measured with the so-called circle method described by Youderian et al. We measured deviation from the premorbid center of rotation (COR), and more than 3mm was considered as minimal clinical important difference. Additionally, pre- and postoperative humeral head diameter (HHD), head neck angle (HNA) and humeral head height (HHH) were measured to assess additional geometrical risk factors for poor RPHA. RESULTS The mean distance from of the premorbid to the implanted head COR was 4.3mm ± 3.1mm. Thirty five shoulders (35%) showed a deviation of less than 3mm (mean 1.9, ±1.1) and 65 shoulders (65%) a deviation of ≥3mm (mean 8.0 ± 3.7). Overstuffing was the main reason for poor RPHA (88%). The level of the humeral head cut was responsible for overstuffing in the 46 of the 57 overstuffed cases. The preoperative HHD, HHH and the HNA were significantly larger, higher and more in valgus angulation in the group with accurate compared to the group with poor RPHA (HHD of 61.1mm ±4.4 vs 55.9 ±6.6, p<0.001; HHH 8.6±2.2 vs 7.6±2.6 p=0.026, varus angulation of 134.7° ±6.4° vs. 131.0° ±7.91, p=0.010). CONCLUSION Restoration of proximal humeral anatomy after stemless TSA using CT-based 3D planning was not precise. A poorly performed humeral head cut was the main reason for overstuffing which was seen in 88% of the cases with inaccurate RPHA. Preoperative small HHD, low HHH and varus angulated HNA are risk factors for poor RPHA after stemless TSA. CLINICAL SIGNIFICANCE While Preoperative CT-based 3-D planning gives insight into the proximal humeral anatomy, execution of this insight through visual based surgery without guides or navigation, does not appear to increase accuracy of RPHA. LEVEL OF EVIDENCE Level IV; Case Series; Treatment Study.